Certain microstructured optical products, such as those described U.S. Pat. Nos. 5,175,030 (Lu et al.), 5,183,597 (Lu), 5,917,664 (O'Neill et al), 5,919,551 (Cobb, Jr. et al.), 6,111,696 (Allen et al.), 6,280,063 B1 (Fong et al.), 6,356,39 B1 (Gardiner et al.), can be referred to as structured optical films or light management films. Light management films can include, for example, brightness enhancement films, reflective films, turning films, and the like. These light management films have a variety of uses. For example, brightness enhancement films can be used in electronic products to increase the brightness of a backlit flat panel display such as a liquid crystal display (LCD) included in electroluminescent panels, laptop computer displays, word processors, desktop monitors, hand-held devices, televisions, video cameras, as well as automotive and aviation displays.
The index of refraction of materials in a brightness enhancement film is often related to the brightness gain (i.e., “gain”) produced when such a film is used with a backlit display. Improved brightness can allow the electronic product to operate more efficiently by using less power to light the display. The use of lower power often can reduce power consumption, can reduce the heat load on the electronic components, and can extend the lifetime of the electronic product. Brightness enhancement films often contain polymeric material with a high index of refraction (e.g., at least 1.4).
The microstructures included in the light management film can be in a variety of forms such as in a series of alternating tips and grooves. In some examples, the light management films have regular, repeating patterns of symmetrical tips and grooves. In other examples, the light management films have tips and grooves that are non-symmetrical. The size, orientation, or distance between the tips and grooves can be uniform or non-uniform.
One drawback of some current light management films is that the tips of the microstructure are susceptible to mechanical damage. For example, light scraping with a fingernail or a hard, relatively sharp edge can cause the tips of the microstructure to break or fracture. Conditions sufficient to break the tips can occur during normal handling of the light management films. For example, the tips of brightness enhancement films can be broken during the process of manufacturing liquid crystal displays that include such films.
When tips of the microstructure are broken, the reflective and refractive properties of the affected tips are reduced and the transmitted light is scattered in virtually all forward angles. When the light management film is a brightness enhancement film on a display, and the display is viewed straight on, areas that contain scratches in the light management film are less bright then the surrounding, undamaged areas of the brightness enhancement film. However, when the display is viewed at an angle near or greater than the cutoff angle (i.e., the angle at which the image on the display is no longer viewable), the areas that contain scratches look substantially brighter than the surrounding, undamaged area of the film. In both situations, the scratches are objectionable from a cosmetic standpoint. Brightness enhancement films with more than a few, minor scratches may be unacceptable for use in some displays such as liquid crystal displays.